This invention relates generally to direct drive servo-valves and more particularly to a direct drive servo-valve in which rotational motion of a motor rotor is converted into linear motion of a spool valve and specifically to a novel drive connection between a shaft of the motor rotor and the spool valve.
Torque motor driven spool valves are well known in the art including such which operate through the utilization of a rotary torque motor having a drive member extending from the rotor thereof into contact with the spool valve to directly reciprocate the spool valve within a bore provided in the valve housing to thereby control the flow of fluid from a source thereof to the load in response to electrical signals applied to the drive motor. Such devices are commonly referred to as direct drive valves and there are various ways of interconnecting the shaft to the spool valve in an eccentric manner so as to convert the limited angle rotary motion of the motor rotor shaft to linear motion of the spool valve.
One example of such a prior art connection is illustrated in U.S. Pat. No. 4,793,377 which discloses the utilization of a spherical tip which is formed integrally with the shaft of the motor rotor and engages the spool valve to control the fluid flow through the valve housing.
Another prior art direct drive valve utilizing a spherical ball drive mechanism is shown in U.S. Pat. No. 4,573,494. Therein disclosed is a spherical bearing assembly which includes an outer race disposed upon the spool valve and a spherical bearing member disposed upon the end of the motor rotor shaft in a slip-fit manner with the outer surface thereof being received within the inner surface of the outer race member.
A further prior art connecting device for the drive member is shown in U.S. Pat. No. 5,052,441 which discloses a ball having a hole drilled therein which receives the end of the eccentrically disposed shaft on the motor rotor with the ball and the shaft brazed together. Typically devices of this type utilize a hardened ball which is required to withstand the frictional wear between the ball and the opening in the spool valve. Because the ball is of hardened material, the hole therein is typically machined by electron-discharged machining (EDM). The shaft extending from the motor rotor is machined to provide a cylindrical post having a diameter such that it is received within the opening formed by EDM in the ball. The utilization of the EDM operation is expensive and leaves a re-melt layer on the ball which must be removed before the post is permanently affixed to the ball by a brazing operation. The removal of the re-melt layer is usually done by lapping which is an expensive operation as is the EDM machining. If the re-melt layer is not completely removed, then the brazing will not accomplish adherence of the ball material to the post on the shaft resulting in a weak braze joint which can in turn cause failures of the direct drive valve during use.
There is thus needed a simple way of providing a spherical ball drive mechanism at the end of the motor rotor shaft for engagement as the drive member for a spool valve on a rotary direct drive valve.
A direct drive servo-valve including a valve housing having a valve spool reciprocally received within a bore provided therein for controlling fluid flow therethrough along with a motor means having a drive member for engagement with the valve spool which drive member includes a shaft having a longitudinal axis and an end defining an eccentrically disposed bore with a ball having an integral protrusion thereon sized such that the protrusion is adapted to be received within the bore with the ball being permanently secured to the shaft.
In accordance with a further aspect of the present invention there is provided a method of manufacturing a direct drive servo valve which includes forming an eccentrically disposed bore in one end of a shaft of a drive member which engages a spool for controlling the flow of fluid, providing a ball, removing a portion of the ball to provide a protrusion thereon and then securing the ball to the end of the shaft in a permanent fashion such as by brazing.